Capacitor and electronic substrate including the same

ABSTRACT

A capacitor including a substrate; a conductive layer provided on the substrate and containing conductive particles; a valve metal sheet having a dielectric part formed throughout an entire surface of the conductive layer; a protection layer covering the valve metal sheet; a first electrode terminal electrically connected to the conductive layer and partially exposed from an external surface of the protection layer; and a second electrode terminal electrically connected to a surface of the valve metal sheet which is opposite to a surface of the valve metal sheet on which the dielectric part is provided, and the second electrode terminal partially exposed from the external surface of the protection layer; wherein the dielectric part is made of an oxide of a metallic material of the valve metal sheet, the dielectric part is formed with a corrugated surface on the conductive layer, and the conductive particles of the conductive layer are in contact with the corrugated surface of the dielectric part.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of Ser. No. 11/857,622,filed Sep. 19, 2007, which is based upon and claims the benefit ofpriority of Japanese patent application No. 2006-254424, filed on Sep.20, 2006, the entire contents of which are herein incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a capacitor, a manufacturing methodthereof, and an electronic substrate including the capacitor, and moreparticularly to a capacitor which is appropriate for a decouplingcapacitor, a manufacturing method of the capacitor, and an electronicsubstrate including the capacitor.

2. Description of the Related Art

In recent years, in semiconductor integrated circuit devices includingmicroprocessors, improvements for increased operating speed and reducedpower consumption are advanced. In order to stabilize operation of asemiconductor integrated circuit device in high frequency areas in GHzbands, at low voltage, it is important to control change of the powersupply voltage due to a rapid change of the load impedance, and toremove high frequency noises of the power supply.

In a conventional semiconductor package substrate, a decouplingcapacitor which is a type of the multi-layered ceramic capacitor (MLCC)is mounted in the vicinity of a semiconductor integrated circuit device,in order to prevent the change of the power-supply voltage and avoid amalfunction of the semiconductor integrated circuit device due to highfrequency noises superimposed on a power-supply line and a ground line.

It is desired that, as the characteristics needed for a decouplingcapacitor, the decoupling capacitor has both a large amount ofcapacitance and a reduced inductance in high frequency areas.

FIG. 1 shows the composition of a conventional thin-film capacitor. Asshown in FIG. 1, the thin-film capacitor 100 has a thin-film dielectriclayer 103, constituting the capacitor, which is proposed for anincreased amount of capacitance.

The thin-film capacitor 100 is manufactured through a thin-filmfabrication process using a vacuum system. In the thin-film fabricationprocess, a lower electrode 102, a dielectric layer 103, and an upperelectrode 104 are deposited on a supporting substrate 101 which is madeof, for example, silicon.

Since performing a micro fabrication using dry etching is possible forthe thin-film capacitor 100, it is possible to make small the wiringlength between the lower electrode or the upper electrode and theterminal 105, and the distance between the terminals. Thus, thisthin-film capacitor 100 can be formed into a capacitor having lowinductance structure. For example, see Japanese Laid-Open PatentApplication No. 2004-214589.

On the other hand, conventionally, a solid electrolytic capacitor isused as a capacitor which has a large capacitance. In the case of thesolid electrolytic capacitor, it is difficult to make small the distancebetween the terminals and the wiring length due to the structurethereof. It is likely that the equivalent series inductance (ESL)increases. And the solid electrolytic capacitor does not function as adecoupling capacitor which is able to operate fully in high frequencyareas. There is proposed a solid electrolytic capacitor which is adaptedfor reducing the ESL or the ESR. For example, see Japanese Laid-OpenPatent Application No. 2005-012084.

However, the thin-film capacitor 100 as disclosed in Japanese Laid-OpenPatent Application No. 2004-214589 has to use an expensive vacuumthin-film forming system, such as a sputtering equipment, as theindispensable installation for forming the lower electrode 102, theupper electrode 104, and the dielectric layer 103. For this reason, themanufacturing cost is increased.

Moreover, the lower electrode 102 and the upper electrode 104 are verythin films on the order of several hundreds nanometers, and it isnecessary to use noble metals, such as Pt and Au, which are hard to beoxidized. For this reason, the material cost is also increased. Inaddition, since the thin films are likely to be short circuited due toinclusion of foreign bodies, such as particles, performing a clearingprocess for surface improvement may be needed for the yield enhancement.Because of the above factors, it is difficult to attain low-costmanufacturing of the thin-film capacitor.

The solid electrolytic capacitor as disclosed in Japanese Laid-OpenPatent Application No. 2005-012084 has a complicated structure. For thisreason, the manufacturing processes are complicated, and it is difficultto attain low-cost manufacturing of the solid electrolytic capacitor.

SUMMARY OF THE INVENTION

In an embodiment of the invention which solves or reduces one or more ofthe above-mentioned problems, there is provided a capacitor including: asubstrate; a conductive layer provided on the substrate and containingconductive compounds; a valve metal sheet having a dielectric partformed throughout an entire surface of the conductive layer; aprotection layer covering the valve metal sheet; a first electrodeterminal electrically connected to the conductive layer and partiallyexposed from an external surface of the protection layer; and a secondelectrode terminal electrically connected to a surface of the valvemetal sheet which is opposite to a surface of the valve metal sheet onwhich the dielectric part is provided, and the second electrode terminalpartially exposed from the external surface of the protection layer;wherein the dielectric part is made of an oxide of a metallic materialof the valve metal sheet, the dielectric part is formed with an unevensurface on the conductive layer, and the conductive compounds of theconductive layer are in contact with the uneven surface of thedielectric part.

In an embodiment of the invention which solves or reduces one or more ofthe above-mentioned problems, there is provided a manufacturing methodof a capacitor, the method including the steps of: forming a dielectricpart by oxidizing an entire first surface of a valve metal sheet;forming a through hole in the valve metal sheet in which the dielectricpart is formed; applying an adhesive conductive material to a surface ofa substrate; attaching the valve metal sheet in which the through holeis formed, to the substrate so that the first surface contacts theconductive material on the substrate surface; forming a conductive layerby curing the conductive material; forming a protection layer whichcovers a second surface of the valve metal sheet which is opposite tothe first surface of the valve metal sheet; forming openings in theprotection layer, so that the conductive layer in the through hole andthe second surface of the valve metal sheet are partially exposed fromthe openings; and filling up the openings in the protection layer withanother conductive material to form electrode terminals.

In an embodiment of the invention which solves or reduces one or more ofthe above-mentioned problems, there is provided an electronic substrateincluding a capacitor, a semiconductor device, and a wiring substrateprovided to connect the capacitor and the semiconductor deviceelectrically, wherein the capacitor comprises: a substrate; a conductivelayer provided on the substrate and containing conductive particles; avalve metal sheet having a dielectric part formed throughout an entiresurface of the conductive layer; a protection layer covering the valvemetal sheet; a first electrode terminal electrically connected to theconductive layer and partially exposed from an external surface of theprotection layer; and a second electrode terminal electrically connectedto a surface of the valve metal sheet which is opposite to a surface ofthe valve metal sheet on which the dielectric part is provided, and thesecond electrode terminal partially exposed from the external surface ofthe protection layer; wherein the dielectric part is made of an oxide ofa metallic material of the valve metal sheet, the dielectric part isformed with an uneven surface on the conductive layer, and theconductive particles of the conductive layer are in contact with theuneven surface of the dielectric part.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

FIG. 1 is a cross-sectional view of a conventional thin-film capacitor.

FIG. 2 is a perspective view of a capacitor in an embodiment of theinvention.

FIG. 3 is a plan view of the capacitor shown in FIG. 2.

FIG. 4 is a cross-sectional view of the capacitor taken along the lineA-A indicated in FIG. 3.

FIG. 5 is an expanded cross-sectional view of the principal part of thecapacitor in this embodiment.

FIG. 6A is a diagram showing a manufacturing method of a capacitor in anembodiment of the invention.

FIG. 6B is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 6C is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 6D is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 6E is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 6F is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 6G is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 6H is a diagram showing a manufacturing method of the capacitor inthis embodiment.

FIG. 7 is a plan view of the capacitor in the case of example 1.

FIG. 8 is a plan view of the capacitor in the case of example 2.

FIG. 9 is a diagram showing the impedance characteristics of thecapacitors in the cases of examples 1 and 2.

FIG. 10 is a cross-sectional view of an electronic substrate in anembodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of an embodiment of the invention withreference to the accompanying drawings.

FIG. 2 is a perspective view of a capacitor in an embodiment of theinvention. FIG. 3 is a plan view of the capacitor shown in FIG. 2. FIG.4 is a cross-sectional view of the capacitor taken along the line A-Aindicated in FIG. 3.

As shown in FIG. 2 through FIG. 4, the capacitor in this embodimentcomprises a substrate 11, a lower electrode 12, a valve metal sheet 15,a protection layer 16, and electrode terminals 20, 21. The lowerelectrode 12 is formed on the substrate 11. The valve metal sheet 15includes an oxide-film dielectric layer 13 formed on the lower electrode12, and an upper electrode 14 formed on the dielectric layer 13. Theprotection layer 16 is provided so that the valve metal sheet 15 isenclosed in the protection layer 16. The electrode terminal 20 and theelectrode terminal 21 are electrically connected to the upper electrode14 and the lower electrode 12, respectively. The electrode terminals 20and 21 are formed by penetrating the protection layer 16.

The electrode terminal 21 connected to the lower electrode 12 is formedthrough the inside of an opening which penetrates the valve metal sheet15 in a thickness direction of the valve metal sheet 15. The electrodeterminals 20 and 21 are formed so that the protection layer 16 ispenetrated by the terminals 20 and 21.

As is described below in detail, the capacitor 10 has a simplecomposition which is constituted by the lower electrode 12, the oxidefilm dielectric layer 13, and the upper electrode 14, and it is possibleto allow yield improvement without the need of expensive manufacturingfacilities.

The substrate 11 may be made of an insulating sheet material which isnot limited to a particular material. For example, the material of thesubstrate 11 is chosen from among a glass substrate, a siliconsubstrate, a glass epoxy group substrate, polyimide resin, etc. Forexample, if the substrate 11 is made of a glass substrate, the thicknessof the substrate 11 may be about 300 micrometers.

The lower electrode 12 is made of a resin material which is about 50micrometers thick and contains conductive particles. For example, aconductive paste may be used to form the lower electrode 12. In theconductive paste, highly conductive particles, such as Ag, Au, Cu, andgraphite, are distributed in a resin material, such as epoxy resin orpolyimide resin.

FIG. 5 is an expanded cross-sectional view of the principal part of thecapacitor in this embodiment. The cross-section of the lamination partof the lower electrode 12, the oxide film dielectric layer 13, and theupper electrode 14 is shown in FIG. 5.

Referring to FIG. 5 as well as FIG. 2 through FIG. 4, the conductiveparticles 12 a contained in the lower electrode 12 are distributed inthe resin material 12 b. It is preferred that the average grain size ofthe conductive particles 12 a is smaller than the average pore diameterof the pores 13 b formed in the surface of the oxide film dielectriclayer 13 which is in contact with the lower electrode 12.

By this composition, the pores 13 b are filled up with the conductiveparticles 12 a sufficiently, the substantial area in which the lowerelectrode 12 and the oxide film dielectric layer 13 touch each otherincreases, and the electrostatic capacitance of the capacitor 10 can beincreased.

It is preferred that the average grain size of the conductive particles12 a is set to be in a range of 2 nm-10 nm according to the size of thepores 13 b of the oxide film dielectric layer 13 so that the pores 13 bcan be filled up sufficiently with the conductive particles 12 a.

With the pores 13 b being filled up with the conductive particlessufficiently, the electrostatic capacitance increases and it isstabilized at a predetermined saturation value according to the surfacedensity and size of the pores of the oxide film dielectric layer 13.Thus, the setting of the electrostatic capacitance of the capacitor canbe easily carried out.

It is preferred that the resistibility of the lower electrode 12 afterthe curing of the conductive paste is 10 μΩcm or less, in order to avoidincreasing of the resistance of the capacitor too much. Although it ispreferred that the resistibility of the lower electrode 12 is as smallas possible, the lower limit of the resistibility of the lower electrode12 is 0.1 μΩcm, which is equal to the resistibility of Au.

The oxide film dielectric layer 13 is formed in the surface by the sideof the lower electrode 12.

On the surface of the opposite side, the valve metal material isexposed, and it is functioning as the surface on which oxide filmdielectric layer 13 is formed as upper electrode 14.

That is, the oxide film dielectric layer 13 and upper electrode 14 areunified.

The valve metal sheet 15 will be explained later with respect to themanufacturing method of the capacitor. The valve metal sheet 15 isproduced as follows. An oxide layer is formed on one surface of a foilor sheet of the valve metal material by using an anodic oxidationmethod, and this oxidation portion is formed into the oxide filmdielectric layer 13. And the remaining metal portion of the valve metalmaterial which remains non-oxidized is formed into the upper electrode14. Therefore, the oxide film dielectric layer 13 and the upperelectrode 14 are unified, and the respective portions are closely incontact with each other, thereby avoiding physical exfoliation.

As the valve metal material applicable to the valve metal sheet 15,aluminium, tantalum, niobium, titanium, hafnium, zirconium, zinc,tungsten, bismuth, antimony, etc. may be mentioned. Among them, moresuitable materials for the valve metal sheet 15 are aluminium, tantalum,and niobium because they are easily procured. As for the valve metalmaterial, by using the anodic oxidation method, an anodic oxide film ofthe valve metal material can be formed easily, and this oxide filmconstitutes the oxide film dielectric layer 13.

The oxide film dielectric layer 13 is made of an anodic oxidization ofthe valve metal material, and it is an dielectric material. In the oxidefilm dielectric layer 13, unevenness (uneven surface 13 a) is formed onits surface which is in contact with the lower electrode 12. Thisunevenness is formed when the surface of the valve metal sheet 15 isoxidized.

Since the conductive particles of the lower electrode 12 contact theuneven surface 13 a, the oxide film dielectric layer 13 and the lowerelectrode 12 are in close contact with each other, and the total contactarea increases. As a result, the capacitance increases.

The corrugated surface 13 a of the oxide film dielectric layer 13 may beformed as a porous layer. For example, it is desirable that thecorrugated surface 13 a is formed as a porous layer in which the poresthe average pore diameter of which is in a range of 100 nm-500 nm aredistributed.

As will be explained later, the corrugated surface 13 a can be formed byan electrolytic etching process. In this case, the contact area betweenthe oxide film dielectric layer 13 and the lower electrode 12 increaseswith the pores being filled up with the conductive paste of the lowerelectrode 12.

The upper electrode 14 is 50 micrometers thick, for example. The upperelectrode 14 is constituted by the metal part of the valve metal sheet15. The metal part is made of any of the valve metal materials mentionedabove.

As a suitable protection layer, benzocyclobutene resin, polyimide resin,epoxy resin, bismaleimide resin, maleimide resin, cyanide resin,polyphenylene ether resin, polyphenylene oxide resin, fluorinecontaining resin, liquid crystal polymer, polyetherimide resin, andpolyetheretherketone resin are mentioned. It is preferred that theprotection layer is made of a photosensitive resin. If a photosensitiveresin is selected, formation of an excessive photoresist layer and theetching process which are needed to form openings in the protectionlayer in the case of another resin can be omitted.

The electrode terminal 20 and the electrode terminal 21 are made of anconductive material, such as Sn—Ag solder. They contact the surface ofthe upper electrode 14 and the surface of the lower electrode 12,respectively, and they are electrically connected together.

The electrode terminal 20 and the electrode terminal 21 are formed withthe plating seed layer 18 (which will be described later), and theplating seed layer 18 is provided on the surface of each of the openingsof the lower electrode 12, the upper electrode 14, and the protectionlayer 16 which are filled up with the electrode terminal material.

The electrode terminal 21 connected to the lower electrode 12 iselectrically insulated by the protection layer, in order to avoidcontact with the oxide film dielectric layer 13 and the opening of theupper electrode 14.

As shown in FIG. 3, the electrode terminals 20 and 21 are arranged in alattice formation. The electrode terminals 21 connected to the lowerelectrode 12 and the electrode terminals 20 connected to the upperelectrode 14 are alternately arranged in each of two orthogonaldirections (or X-axis and Y-axis directions) of the capacitor 10.

The above arrangement of the electrode terminals allows the mutualinductance which is generated between electrode terminal 20 and 21according to the electric current flowing through the electrodeterminals 20 and 21, to be canceled by each other. Therefore, theimpedance of the capacitor in high frequency ranges, especially in highfrequency ranges of 1 GHz or more, can be reduced.

Of course, the arrangement of the electrode terminals may be modifiedsuch that the electrode terminals 20 connected to the lower electrodes12 are arrayed in a row (in the X-axis direction), and the electrodeterminal 21 connected to the upper electrodes 14 are arrayed in a row(in the X-axis direction), and these rows are alternately arranged incolumns in the direction of the Y-axis. Of course, this arrangement maybe changed to the arrangement in which the direction of the X-axis andthe direction of the Y-axis are reversed.

As explained above, the capacitor 10 in this embodiment is provided sothat the valve metal sheet 15 has the oxide film dielectric part 31which is made of the oxide of the valve metal material and covers theentire surface of one of the upper and lower surfaces of the valve metalsheet 15, and has the upper electrode 14 which is provided on the othersurface of the upper and lower surfaces of the valve metal sheet 15.

The conductive particles of the lower electrode 12 contact the unevensurface 13 a of the surface of the oxide film dielectric layer 13sufficiently. As a result, the use of expensive materials, such as noblemetals, is unnecessary and the complicated structure is alsounnecessary. Therefore, the cost of the capacitor 10 can be reduced.

Next, a manufacturing method of a capacitor in an embodiment of theinvention will be explained with reference to FIG. 6A through FIG. 6H.

FIG. 6A through FIG. 6H are diagrams for explaining the manufacturingmethod of the capacitor in this embodiment.

First, at the step of FIG. 6A, a valve metal sheet (for example, analuminum foil or an aluminum sheet) is prepared, and one surface of thevalve metal sheet is oxidized to form an oxide film dielectric layer 13(oxide film dielectric part formation process). As the oxidation methodof the valve metal sheet, an anodic oxidation method and an oxygenplasma etching process are mentioned.

For example, in the case of the anodic oxidation method, a valve metalsheet (for example, an aluminum foil) is immersed in any of a sulfuricacid bath, a phosphoric acid bath, an oxalic acid bath and an adipicacid ammonium bath, one surface of the aluminum foil is used as ananode, and a carbon or platinum electrode is used as a cathode. And thecathode is immersed in the bath, and a given voltage is applied betweenthe anode and the cathode. When the anodic oxidation method is used, onesurface of the aluminum foil is changed into an amorphous alumina and itforms the oxide film dielectric layer 13. On the opposite surface of thealuminum foil which is opposite to the surface in which the oxide filmdielectric layer 13 is formed.

When the oxygen plasma etching process is used, one surface of the valvemetal sheet 15A is exposed to the oxygen ions which are electricallydissociated through generation of the plasma in the oxygen environment,so that the oxide film dielectric layer 13 is formed.

A surface roughing process may be performed prior to the oxide filmdielectric part formation process of FIG. 6A, so that the surface whichwill be formed as the oxide film dielectric layer 13 of the valve metalsheet 15A is roughened (the surface roughing process). As the surfaceroughing process, an electrolytic etching process or an chemical etchingprocess may be used. The electrolytic etching process is preferred inthat it can form the treating surface into a porous layer, and itssurface area can be increased.

In the electrolytic etching process, the well-known processingconditions may be used. For example, a mixed solution of 8% by weighthydrochloric acid and 1% by weight sulfuric acid is used as theelectrolytic etching liquid, the etching temperature is 50 degrees C.,and the applied voltage is set as the sine wave alternating currentvoltage so that the frequency is 20 Hz, the current density 180 mA/cm²,and the electrolysis time is 270 seconds.

When the electrolytic etching process is used, a protection layer, suchas a resist layer, is formed beforehand on the surface of the valvemetal sheet which is not roughened, and the protection layer is removedfrom the valve metal sheet surface after the surface roughing process.

Subsequently, at the step of FIG. 6B, the through holes, which willpenetrate the lower electrode at a subsequent process, are formed in thevalve metal sheet (through hole formation process).

The formation of the through holes is not limited to a specific process.It is sufficient that the formation process is to form the through holesabout 100 micrometers in diameter in the valve metal sheet. For example,a punching process or a laser-beam-machining method may be used as thethrough hole formation process.

The sequence of the step of FIG. 6A and the step of FIG. 6B can bereversed. That is, the steps may be performed in order of the throughhole formation process and the oxide film dielectric part formationprocess. Alternatively, the steps may be performed in order of the oxidefilm dielectric part formation process and the through hole formationprocess.

On the other hand, at the step of FIG. 6C, an adhesive conductivematerial is applied to the substrate. For example, a conductive paste isused as the adhesive conductive material. As mentioned above, in theconductive paste, the highly conductive particles, such as Ag, Au, Cu,or graphite, are distributed in the resin, such as epoxy resin orpolyimide resin.

It is preferred that the average grain size of the conductive particlescontained in the conductive paste is set to be in a range of 2 nm-10 nmaccording to the size of the pores 13 b of the oxide film dielectriclayer 13 so that the pores 13 b can be filled up sufficiently with theconductive particles.

It is preferred that the content of the conductive particles containedin the conductive paste is set to be in a range of 50% by weight-80% byweight, so that good electric conductivity is attained. It is preferredthat the conductive paste has the viscosity at 25 degrees C. in a rangeof 40 Pa-s-120 Pa-s, so that good spreading characteristic is attained.

Subsequently, at the step of FIG. 6D, the valve metal sheet 15 preparedat the step of FIG. 6B and the substrate 11 to which the conductivepaste 12 a is applied at the step of FIG. 6C are attached together. Atthis time, the attaching is performed so that the conductive paste 12 aand the oxide film dielectric layer 13 of the valve metal sheet 15 arein contact with each other.

Before the valve metal sheet 15 and the substrate 11 to which theconductive paste 12 a is applied are attached together, a conductivepolymer may be applied so that the surface of the oxide film dielectriclayer 13 may be covered by the conductive polymer. By this conductivepolymer, the unevenness of the surface of the oxide film dielectriclayer 13 is filled up with the conductive polymer, and a smooth surfaceis formed. Thereby, the adhesion of the valve metal sheet 15 and theoxide film dielectric layer 13 can be increased.

Simultaneously, the conductive polymer enters more easily than theconductive paste 12 a, into the inside of the concave portions of thesurface of the oxide film dielectric layer 13, the contact area of theoxide film dielectric layer 13 and the lower electrode is increased, sothat the capacitance can be increased.

Applying of the conductive polymer is effective especially when theabove-mentioned surface roughing process is performed.

Moreover, at the process of FIG. 6D, the conductive paste 12 a is curedso that the lower electrode 12 is formed. Thereby, the lower electrode12, the oxide film dielectric layer 13, and the upper electrode 14 areformed.

Subsequently, at the step of FIG. 6E, a protection layer 16 which ismade of a resin material is formed on the surface of the structure ofFIG. 6D. It is preferred that the formation of the protection layer isperformed by using a photosensitive resin solution (for example,photosensitive polyimide resin or photosensitive epoxy resin), so thatit facilitates formation of openings at the following process, andformation of an excessive resist layer and the etching process can beomitted.

Moreover, at the step of FIG. 6E, the openings 16 a and 16 b are formedat the predetermined positions on the surface of the protection layer16. The openings 16 a and 16 b are arranged in a lattice formation sothat the surfaces of the lower electrode 12 and the upper electrode 14may be partially exposed, and the electrode terminals may be arranged asshown in FIG. 3.

In this process, when the oxide film (for example, the oxide film formedin the case of the anodizing) is formed on the surface of the upperelectrode 14 (or the surface of the valve metal sheet 15), a dry etchingprocess may be performed to remove the oxide film layer.

Subsequently, at the step of FIG. 6F, a metal-plating seed layer 18 a isformed on the surface of the protection layer of FIG. 6E and the insidesurfaces of the openings (the inside walls and the lower electrode andupper electrode surfaces). Specifically, the metal-plating seed layer 18a is made of a Ti film, a Cu film, and a nickel film which are formedsequentially by a sputtering process, a vacuum deposition process or anon-electrolytic plating.

Subsequently, at the step of FIG. 6G, a resist layer 25 is formed whichcovers the surface of FIG. 6F, and the pattern which has the openings 16a and 16 b at the locations where the electrode terminals will be formedat the following process, in the resist layer 25. Moreover, at the stepof FIG. 6G, the openings 16 a and 16 b are filled up with the conductivematerial (for example, Sn—Ag solder) by performing the electroplatingprocess using the metal-plating seed layer 18 a as the electric supplylayer.

Subsequently, at the step of FIG. 6H, the resist layer 25 shown in FIG.6F is removed, and the solder balls 20 and 21 are formed by performing areflow process as shown in FIG. 6H. Moreover, an excessive metal-platingseed layer is removed by the dry etching process. The capacitor is thusformed.

According to the manufacturing method of the capacitor in thisembodiment, the vacuum process is not used when forming the lowerelectrode 12, the oxide film dielectric layer 13, and the upperelectrode 14. The manufacture cost can be reduced in contrast to that ofthe conventional thin-film capacitor mentioned above. Moreover, areduction of the yield by contamination, such as particles, can be alsoavoided, and the manufacturing cost of the capacitor can be reduced.

Next, some examples of the capacitor in the present embodiment will beexplained.

FIG. 7 and FIG. 8 are plan views of the capacitors in the cases ofexamples 1 and 2 respectively, when viewed from the electrode terminalside.

As shown in FIG. 7, the capacitor 30 in the case of example 1 has thecomposition that is the same as that of the capacitor in the aboveembodiment. The capacitor 30 is in the shape of a 1.8 mm by 1.6 mmrectangle, and the electrode terminals 31 and 32 are arranged in alattice formation in four rows and four columns.

In the capacitor 30 in the case of example 1, the electrode terminals 31connected to the upper electrodes and the electrode terminals 32connected to the lower electrodes are arranged alternately each other.The gap in the lengthwise direction and the transverse direction betweenthe electrode terminals is set to 400 micrometers, and the diameter ofeach electrode terminal is set to 180 micrometers.

As shown in FIG. 8, the capacitor 40 in the case of example 2 has thecomposition that is the same as that of the capacitor in the aboveembodiment. The capacitor 40 is in the shape of a 1.8 mm by 1.6 mmrectangle, and the electrode terminals 41 and 42 are arranged in alattice formation in seven rows and eight columns.

In the capacitor 40 in the case of example 2, the electrode terminal 41connected to the upper electrodes and the electrode terminal 42connected to the lower electrodes are arranged alternately both in thelengthwise direction and the transverse direction. The gap in thelengthwise direction and the transverse direction between the electrodeterminals is set to 200 micrometers, and an the diameter of eachelectrode terminal is set to 100 micrometers.

FIG. 9 is a diagram showing the impedance characteristics of thecapacitors in the cases of examples 1 and 2. In FIG. 9, the verticalaxis denotes the impedance, the horizontal axis denotes the frequency,and the values of both are in logarithmic scale.

As shown in FIG. 9, it is found out that the impedance in the case ofexample 2 is lower at high frequencies than that in the case of example1, and both the equivalent series resistance and the equivalent seriesinductance in the case of example 2 are lower than those in the case ofexample 1. The equivalent series inductance in the case of example 1 is34 pH, and the equivalent series inductance in the case of example 2 is0.3 pH. This is because the reduced electrode terminals in the case ofexample 2 are arranged more densely than in the case of example 1, andthe arrangement of the electrode terminal 41 connected to the upperelectrodes and the electrode terminals 42 connected to the lowerelectrodes are alternate in both the lengthwise direction and thetransverse direction.

According to another consideration of the inventors, it is turned outthat, when the arrangement of the electrode terminals connected to theupper electrodes and the electrode terminals connected to the lowerelectrodes in the case of example 1 is made with the same electrodeterminal diameter and the same spacing interval as in the case ofexample 2, the frequency at which the impedance is at the minimum in thecase of example 1 is about 1/10 times that in the case of example 2.Namely, it is found out that, by using the alternate arrangement of theelectrode terminals 41 connected to the upper electrodes and theelectrode terminals 42 connected to the lower electrodes in the case ofexample 2 both in the lengthwise direction and the transverse direction,it is possible to make the inductance at high frequencies reduced moreeffectively.

Next, a capacitor in the case of example 3 according to the aboveembodiment is produced as follows. First, a perforating process isperformed to a 0.2-mm thick aluminum foil by using the laser beammachining process, so that the through holes (120 micrometers in thediameter) are formed. The arrangement of the through holes isessentially the same as the arrangement of the electrode terminals 21connected to the lower electrodes shown in FIG. 3.

After the aluminum foil in which the through holes are formed is washedwith nitrate fluoride and distilled water, the anodizing process isperformed in the solution in which 150 g of adipic acid ammonium isdissolved to 1 liter of pure water, and the aluminum oxide film isformed on one surface of the aluminum foil. The temperature of thesolution of the anodizing is set to 85 degrees C., the formation voltageis set to 100V, the electric current is set to 0.3 A, and the voltageapplication time is set to 20 minutes.

Subsequently, the silver nano paste is applied in the thickness of 10micrometers to the surface of a glass substrate, and the aluminum foilon which the aluminum oxide film is formed is attached to the glasssubstrate so that the surface of the aluminum oxide film is adhered tothe surface where the silver nano paste is applied, and they are bondedtogether.

Subsequently, the glass substrate to which the aluminum foil is bondedis subjected to the heating process for 1 hour at 200 degrees C. in theatmosphere, so that the silver nano paste is cured.

Subsequently, the photosensitive epoxy resin is applied to the surfaceof the aluminum foil, so that the photosensitive epoxy resin layer isformed. Specifically, an epoxy varnish is applied through the spin coatprocess with the rotation speed is set to 2000 rpm and the applying timeis set to 30 seconds, so that the photosensitive epoxy resin layer withthe thickness of 10 micrometers is formed.

After the pre-baking (the heating temperature: 60 degrees C.) of thephotosensitive epoxy resin layer is performed, the openings for makingthe surfaces of the upper electrode and the lower electrode be exposedare arranged in a lattice formation through the exposure and developmentprocess. The arrangement of the openings is essentially the same as thearrangement of the previously described electrode terminals as shown inFIG. 3.

Moreover, the final baking process (the heating temperature: 200 degreesC.) is performed, the epoxy resin layer is cured, and, finally theprotection layer of the epoxy resin layer with the thickness of 5micrometers is formed.

Subsequently, a Ti film (300 nm thick) and a Cu film (200 nm thick) areformed on the openings and the surfaces of the epoxy resin layer throughthe sputtering process, and a nickel metal-plating film (5 micrometersthick) is formed thereon through the non-electrolytic plating process.Thereby, the under bump metal (UBM) layer which is made of the Ti film,the Cu film and the nickel metal-plating film is formed.

Subsequently, the resist layer which has the openings in which theopenings of the above-mentioned protection layer are exposed is formed,a Sn—Ag solder metal-plating film is formed through the electroplatingprocess, the resist layer is removed, and the solder bumps of the Sn—Agsolder metal plating are formed on the surface of the UBM layer throughthe reflow process. Moreover, the unnecessary UBM layer is removedthrough the dry etching process.

In the above-mentioned manner, the capacitor in the case of example 3 isformed. The capacitors are produced in the above-mentioned conditionsusing aluminum foils having various characteristics, and it is found outthat the capacitor having the capacitance density in a range of 0.2microF/cm²-4 microF/cm² and the withstanding voltage in a range of20V-100V is obtained.

Next, a capacitor in the case of example 4 according to the aboveembodiment is produced as follows. First, using the aluminum foil whichis the same as that in the case of example 3, a resist layer is formedon the surface of the aluminum foil on which the aluminum oxide film isnot formed.

The porous structure is formed on the surface of the aluminum foil onwhich the resist layer is not formed, through the electrolytic etchingprocess.

The mixed solution of 8% by weight hydrochloric acid and 1% by weightsulfuric acid is used as the electrolytic etching liquid, the etchingtemperature is set to 50 degrees C., and the applied voltage is set tothe sine wave alternating current. The frequency is set to 20 Hz, thecurrent density is set to 180 mA/cm², and the electrolysis time is setto 270 seconds.

Subsequently, after the resist is removed from the aluminum foil, theanodizing process is performed using the conditions which are the sameas those in the case of example 1, and the aluminum oxide film is formedon the surface of the porous structure layer.

Subsequently, the solution containing polyethylene dioxythiophene andstyrene sulfonic acid is applied to the surface of the aluminum oxidefilm, and the surface is dried. The process of the solution applying andsurface drying is repeated 5 times.

The subsequent processes which are the same as those in the case ofexample 3 are performed, and the capacitor in the case of example 4 isproduced. The capacitors are produced in the above-mentioned conditionsusing the aluminum foils having various characteristics which are thesame as those in the case of example 1, and it is found out that thecapacitor having the capacitance density in a range of 10 microF/cm²-50microF/cm² and the withstanding voltage in a range of 3V-50V isobtained.

Next, a capacitor in the case of example 5 according to the aboveembodiment is produced as follows. First, a perforating process isperformed to a 0.15-mm thick niobium foil by using the punching process,so that the through holes (150 micrometers in diameter) are formed. Thearrangement of the through holes is essentially the same as thearrangement of the electrode terminals 21 connected to the lowerelectrodes shown in FIG. 3.

After the niobium foil in which the through holes are formed is washedwith nitrate fluoride and distilled water, the anodizing process isperformed in the phosphoric acid solution, and the niobium oxide film isformed in one surface of the niobium foil. The temperature of thesolution of the anodizing is set to 90 degrees C., the formation voltageis set to 150V, the electric current is set to 0.6 A, and the voltageapplication time is set to 10 minutes.

The subsequent processes which are the same as those in the case ofexample 3 are performed, and the capacitor in the case of example 5 isproduced.

The capacitors are produced in the above-mentioned conditions usingniobium foils having various characteristics, and it is found out thatthe capacitor having the capacitance density in a range of 1microF/cm²-25 microF/cm² and the withstanding voltage in a range of3V-50V is obtained. The dielectric constant of the niobium oxide film isabout 42, and it is larger than the dielectric constant (which is about8) of the aluminium oxide film. Thus, the capacitance of the capacitorin the case of example 5 can be remarkably increased from that of thecapacitor in the case of example 3.

FIG. 10 is a cross-sectional view of an electronic substrate including acapacitor in an embodiment of the invention.

As shown in FIG. 10, the electronic substrate 50 comprises a wiringsubstrate 51, and an LSI chip 52 and a decoupling capacitor 53 which aremounted on the wiring substrate 51.

The wiring substrate 51 has a wiring layer 54 on the surface of thesubstrate or within the surface of the substrate. Although thecomposition of the wiring substrate 51 is not limited to thespecifically disclosed embodiment, the wiring substrate 51 isconstituted by, for example, a multilayer interconnection substrate.

For example, a semiconductor integrated circuit is formed on the LSIchip 52. The LSI chip 52 is constituted by, for example, anapplication-specific integrated circuit (ASIC) or a read-only memory(ROM), etc. The decoupling capacitor 53 has the composition which isessentially the same as that of the capacitor in the previouslydescribed embodiment.

In the electronic substrate 50, the decoupling capacitor 53 iselectrically connected to the LSI chip 52 through the wiring layer, andthe decoupling capacitor 53 is electrically inserted between thepower-supply line and the ground line.

Since the cost of the decoupling capacitor 53 according to the inventionis reduced, the cost of the electronic substrate 50 can also be reduced.Although it is not illustrated, many decoupling capacitors 53 are neededfor the LSI chip 52, and the low-cost manufacturing of the decouplingcapacitors 53 will contribute to the low-cost manufacturing of theelectronic substrate 50 considerably.

The present invention is not limited to the specifically disclosedembodiment, and variations and modifications may be made withoutdeparting from the scope of the present invention.

1. A capacitor comprising: a substrate; a conductive layer provided onthe substrate and containing conductive particles; a valve metal sheethaving a dielectric part formed throughout an entire surface of theconductive layer; a protection layer covering the valve metal sheet; afirst electrode terminal electrically connected to the conductive layerand partially exposed from an external surface of the protection layer;and a second electrode terminal electrically connected to a surface ofthe valve metal sheet which is opposite to a surface of the valve metalsheet on which the dielectric part is provided, and the second electrodeterminal partially exposed from the external surface of the protectionlayer; wherein the dielectric part is made of an oxide of a metallicmaterial of the valve metal sheet, the dielectric part is formed with acorrugated surface on the conductive layer, and the conductive particlesof the conductive layer are in contact with the corrugated surface ofthe dielectric part.
 2. The capacitor according to claim 1, wherein thecorrugated surface of the dielectric part is formed as a porous layercontaining pores which are filled up with the conductive particles ofthe conductive layer.
 3. The capacitor according to claim 1, wherein thedielectric part of the valve metal sheet is formed by an anodic oxidefilm of a metallic material of the valve metal sheet.
 4. The capacitoraccording to claim 1, wherein the valve metal sheet is in the form of afoil or a sheet.
 5. The capacitor according to claim 1, wherein themetallic material of the valve metal sheet is made of a metallic elementselected from a group of metallic elements including aluminium,tantalum, niobium, titanium, hafnium, zirconium, zinc, tungsten,bismuth, and antimony.
 6. The capacitor according to claim 1, whereinthe conductive particles of the conductive layer are made of a materialselected from among Ag, Au, Cu, and graphite.
 7. The capacitor accordingto claim 1, wherein the first electrode terminal is provided in athrough hole of the valve metal sheet, and a gap between the firstelectrode terminal and an inside surface of the through hole is filledup with the protection layer.
 8. The capacitor according to claim 1,wherein a plurality of the first electrode terminals and a plurality ofthe second electrode terminals are arranged in a lattice formation onthe protection layer surface, and the first electrode terminals and thesecond electrode terminals are alternately arranged in each of twoorthogonal directions.
 9. An electronic substrate including a capacitor,a semiconductor device, and a wiring substrate provided to connect thecapacitor and the semiconductor device electrically, wherein thecapacitor comprises: a substrate; a conductive layer provided on thesubstrate and containing conductive particles; a valve metal sheethaving a dielectric part formed throughout an entire surface of theconductive layer; a protection layer covering the valve metal sheet; afirst electrode terminal electrically connected to the conductive layerand partially exposed from an external surface of the protection layer;and a second electrode terminal electrically connected to a surface ofthe valve metal sheet which is opposite to a surface of the valve metalsheet on which the dielectric part is provided, and the second electrodeterminal partially exposed from the external surface of the protectionlayer; wherein the dielectric part is made of an oxide of a metallicmaterial of the valve metal sheet, the dielectric part is formed with acorrugated surface on the conductive layer, and the conductive particlesof the conductive layer are in contact with the corrugated surface ofthe dielectric part.